The paramount goal of a fluid management system is that it not leak. Leaky fluid management systems disadvantageously require repairs or fluid replenishment. A secondary goal is that the fluid management system be as small as possible. A third goal is that fabrication costs are low. A fourth goal is that the production time is short. An ideal fluid management system is leakless, small, inexpensive, and rapidly made.
Small spacecraft use propulsion systems that utilize stored fluids. A small propulsion system is a form of a fluid management system that is useful for miniature satellites. Propulsion for miniature spacecraft, such as picosatellites and nanosatellites, requires a fluid management system that is preferably leakless, small, inexpensive, and rapidly made. For an example of a small spacecraft see “The Design and Test of a Compact Propulsion System for CanX Nanosatellite Formation Flying,” Stephen Mauthe, et al., 19th Annual Conference on Small Satellite, Logan Utah, 2005. Propulsion units are typically constructed by assembling distinct functional components such as tanks, valves, and tubing with fittings, generally designated as internal plumbing. For reliability, it is desirable to minimize the number of fittings because each fitting is a potential leak location. Also, each fitting requires a means for sealing. Miniature satellites often do not provide adequate room for wrenching the fitting nuts tight, thereby presenting an assembly challenge that is often solved by spacing parts far apart. When the parts are spaced far apart, then space is wasted inside the miniature spacecraft making it not so miniature. When the parts joined by fittings happen to be of different materials, then a coefficient of expansion mismatch may also cause leakage. When the joints between components are sealed by welding or bonding rather than wrenching, then the assembly still must be designed with some consideration for adequate access to the joints, which typically results in a less then optimal packaging efficiency. When tubing must be bent to follow a permissible path from a tank to a valve or thruster nozzle, then the tube must be bent accurately and precisely, which is a difficult, time consuming, and therefore costly task.
A prior art solution to the problem of sealing tubing joints and bending tubes precisely is a laminate structure whereby channels create a manifold to move fluids from one place to another are etched into layers of metal or plastic. U.S. Pat. No. 6,334,301, issued to Otsap on Jan. 1, 2002, entitled “Assembly of Etched Sheets Forming a Fluidic Module” teaches layering to form a fluidic module using chemical etching. U.S. Pat. No. 6,645,432, issued to Anderson on Nov. 11, 2003, entitled “Microfluidic Systems Including Three-Dimensionally Arrayed Channel Networks” teaches making sealed channels using molded layers. The layers are diffusion bonded or glued to one another with the benefit of a much larger surface area for the bond and therefore less likelihood of leaking. Each layer of the manifold is etched or machined and must be successfully bonded to its neighboring layers. This assembly method is methodical and expensive with no guarantee that the bonding will be successful and leak free. The use of bonded layers creates an opportunity for leaks in between the bonded layers. The thickness of the layers will also determine the smoothness of any curved surface of three-dimensional paths, such as channels and tubes that extend between layers. Multiple layers that are bonded together do not always provide for desirable smooth surfaces, with several layers forming jagged curved surfaces. A prior solution for making microfluidic three-dimensional systems used bonded layers to adhere layers together to form internal three-dimensional fluid paths. The layers were etched or molded and then joined together. The assembly method for fabricating a complete module disadvantageously requires fabricating each layer separately and bonding each in turn to form the module.
A prior art method for creating structures and fluid transport elements in a monolithic structure is by using concentrated UV light to expose photosensitive glass. U.S. Pat. No. 5,374,291, issued to Yabe on Dec. 20, 1994 entitled “Method of processing Photosensitive Glass” teaches photoetching of glass. U.S. Pat. No. 6,783,920, issued to Livingston, entitled “Photosensitive Glass Variable Laser Exposure Patterning Method”, teaches making sealed channels in ceramic photosensitive materials. The process begins with a solid block of glass that has the correct properties in order to respond to the laser developing. A laser spot can be positioned in three dimensions by a computer controlled program that is used to write the desired internal patterns, thereby developing channels within the block. The developed areas are then removed by chemically etching. In this method, when a large volume must be removed, then the process is disadvantageously a time consuming process.
Computer aided design software has been used to rapidly make solid mechanical models and prototypes. Computer controlled rapid additive prototyping machines and materials have made three-dimensional fluidic modules. The computer aided design software can run on personal computers providing the capability to create a part that is impossible to make when only traditional subtractive machining is used. When using rapid prototyping by an additive production method, a three-dimensional part or module can be made quickly. Historically, additive rapid prototyping was used to fit check parts that would later be produced as production parts by injection molding or even subtractively machined. Historically, the quality of the prototyping part was dimensionally imprecise and the material was grainy and brittle, generally unsuitable for long term fluidic plumbing use.
However, in recent years, new rapid prototyping machines, processes and materials have been used. The speed and accuracy of the rapid prototyping models are improving. The quality and ease of using the computer software has also improved as well. It has now become easy to create complex three-dimensional rapid prototyping models and objects. The rapid prototyping by designers is carefully done so that the prototype design can be manufactured by final manufacturing processes, which are different than the rapid prototyping processes. Most notably, the cost of the prototyping machines has been reduced and the quality and variety of the prototyping materials has increased.
One type of rapid prototyping is the additive rapid prototyping process that typically uses a powder or liquid resin that is laid down and cured. Powder metals have also been used in rapid prototyping processes for creating metal models. In the additive rapid prototyping process, a computer model of the three-dimensional prototype part is computationally sliced up into layers of equal thickness, typically a few thousandths of an inch thick. The layers are digitally patterned, without the use of masks to lay down layers in sequence. The prototype part is thus additively built by separately laying down each of many thin layers on top of a prior layer and curing the material so that the layers adhere together in a permanent manner. In this way, the layers are patterned and laid down in sequence. The prototyping parts created by additive rapid prototyping are used for prototyping an object that might end up as an injected molded production part upon the final manufacturing production runs. The rapid prototyping allows engineers to inspect and examine the prototype part prior to the relatively expensive step of creating a mold to make final manufactured production parts. A few instances have emerged where rapid prototyping parts are used directly as a finished product. However, some prototyping materials are brittle and unsuitable for use in fluidic systems.
Prior art fluidic modules having small dimensions are difficult to produce. Prior art methods of bonding together successive layers to form a three-dimensional part suffer from unwanted gaps and voids that may be unsuitable for use in fluidic systems. Laser exposed photoceramic glasses require extensive evacuation steps restricted to expensive photostructurable materials. Additive rapid prototyping have used brittle and grainy materials that are unsuitable for use in fluidic systems. These and other disadvantages are solved or reduced using the invention.